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*Author to whom all correspondence and reprint requests should be addressed.
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Abstract
Corn steep liquor (CSL), a byproduct of the corn wet-milling process, was
used in an immobilized cell continuous biofilm reactor to replace the expen-
sive P2 medium ingredients. The use of CSL resulted in the production of
6.29 g/L of total acetone-butanol-ethanol (ABE) as compared with 6.86 g/L
in a control experiment. These studies were performed at a dilution rate of
0.32 h–1 ,9333
. The productivities in the control and CSL experiment were 2.19
and 2.01 g/(L·h), respectively. Although the use of CSL resulted in a 10%
decrease in productivity, it is viewed that its application would be economi-
cal compared to P2 medium. Hence, CSL may be used to replace the P2
medium. It was also demonstrated that inclusion of butyrate into the feed
was beneficial to the butanol fermentation. A control experiment produced
4.77 g/L of total ABE, and the experiment with supplemented sodium buty-
rate produced 5.70 g/L of total ABE. The butanol concentration increased
from 3.14 to 4.04 g/L. Inclusion of acetate in the feed medium of the immo-
bilized cell biofilm reactor was not found to be beneficial for the ABE fermen-
tation, as reported for the batch ABE fermentation.
Index Entries: Immobilized cell biofilm reactor; butanol; corn steep liquor;
sodium butyrate; Clostridium beijerinckii BA101; sodium acetate.
†
Names are necessary to report factually on available data. However, the USDA neither
guarantees nor warrants the standard of the product, and the use of the names by USDA
implies no approval of the product to the exclusion of others that may also be suitable.
Introduction
Butanol, an industrially important chemical, can be produced by fer-
mentation of carbohydrates using various solventogenic clostridia. In fact,
this fermentation was commercially viable until after World War II when
petrochemically produced butanol became available at competitive prices
(1). For several reasons, including fluctuating oil prices and the depletion
of oil reserves, intensive research efforts on this fermentation have been
made. Recent technological developments including the development of
superior cultures, productive reactors, and efficient downstream process-
ing have once again made this fermentation attractive. Although these
developments are encouraging, certain problems, such as the use of eco-
nomical substrates, need to be resolved before this fermentation will be
able to become commercially viable.
The use of continuous immobilized cell biofilm reactors eliminates
downtime and hence results in superior reactor productivity (2,3).
Adsorbed cell continuous biofilm reactors have been shown to favorably
affect process economics (4). Application of these reactors reduces capital
and operational cost, thus making the process simpler. Within these reac-
tors, cells are immobilized by adsorption, which is a simpler technique than
other techniques such as entrapment and covalent bonding (5). Adsorption
is a simple technique and can be performed inside the reactors without the
use of chemicals, whereas entrapment and covalent bonding are compli-
cated techniques and require chemicals for bond formation. In anaerobic
systems, such as butanol production, adsorption can be performed anaero-
bically within the reactor. An additional advantage of adsorption is that
cells form uniform biofilm layers around the support, which lessens diffu-
sion resistance compared to entrapped and covalently bonded cells. Hence,
these reactors are called biofilm reactors. Because of reduction in diffusion
resistance, the reaction rate is enhanced. For this reason, adsorption was
chosen as the technique to be employed for Clostridium beijerinckii BA101